Named after a Union spy ring in the Civil War, the Secret Service was founded in 1865 to fight counterfeiting. It began protecting presidents informally in 1894, when “suspicious persons who might be Western gamblers, anarchists, or cranks” allegedly hatched a plot to kill Grover Cleveland. Technically, though, the Secret Service had no authority to protect the president, and, in one of the more vivid examples of the inherent animosity between the legislative and executive branches, Congress was loath to grant it. Even the murders of three presidents – Lincoln, Garfield, and McKinley – did not move Congress to authorize presidential bodyguards. Some lawmakers feared a president with imperial inclinations could turn his protective force into a private army that he could use to impose his will. There was also something decidedly un-American about surrounding a president with bodyguards. As an early twentieth-century children’s primer put it:

How are emperors and kings protected?
By great troops of guards; so that it is difficult to approach them. How is the president guarded?
He needs no guards at all; he may be visited by any person like a private citizen.

Over the years, the Secret Service’s informal protection of presidents gradually became institutionalized, though, incredibly, it remained technically illegal. During World War II, as many as a hundred agents were assigned to President Roosevelt, yet none were assigned to his first two vice presidents. In fact, vice presidents had never received Secret Service protection. This struck Harry Truman’s military aide, Harry Vaughn, as incongruous, especially in light of Roosevelt’s failing health. Vaughn asked Treasury Secretary Henry Morganthau, who oversaw the Secret Service, if it would be possible to assign agents to Truman.

The Secret Service, long accustomed to protecting Franklin Roosevelt, a president who was largely immobile, who literally couldn’t move without their assistance, had to make some major adjustments when Truman moved into the White House. “So, we had to revise our thinking,” said Floyd Boring, an agent assigned to both Roosevelt and Truman, “and the whole strategy of the place changed because of his ability to be in movement and motion.”

A few days after becoming president, Truman realized he needed some pocket money, so he bounded out of the Oval Office, out the front door of the White House, down the driveway, and through the wrought-iron gate. He was going to the bank. Robert G. Nixon, a reporter assigned to the White House, remembered the scene. “The astonished Secret Service did a double take. … They couldn’t believe this was happening. He took them completely by surprise.”

Several agents finally caught up with the president on Pennsylvania Avenue, near Fifteenth Street. Truman, said Nixon, was given “a little talking to” by the head of his security detail. He was told he could go nowhere alone – except the bathroom. Throughout his presidency, Truman would walk to the bank to deposit his presidential paycheck – but never by himself.

Truman’s morning walks were particularly troublesome to his Secret Service detail. (The one pictured above is from 1950.) Four agents were assigned to accompany him, one at the front, one on each side, and one at the back. The poor agent at the front – the point man – simply had to guess which way Truman was headed. Often he guessed wrong. “We lost a few of them that way,” remembered Floyd Boring.

The presidential walks inevitably created potentially dangerous situations, particularly considering Washington’s notoriously bad drivers. To keep Truman from getting run over while crossing the street, the Secret Service came up with an ingenious solution. The traffic lights around the White House were rigged so they could be turned red in all directions whenever the ambulating president approached, allowing him to complete his two-mile walk swiftly and safely. It didn’t take long for Truman to notice his peculiar effect on traffic lights, and he put an end to the practice. “I’ll wait for the light like any other pedestrian,” he insisted.

Truman deeply admired his Secret Service agents, and the feeling was mutual. He enjoyed chatting with them on his morning walks. “He would treat us almost like sons,” remembered Rex Scouten, an agent who served on Truman’s detail. “He talked nearly the whole time.” “He never came on as being superior,” recalled Floyd Boring, another Truman agent. “He could talk to anyone! … He never got swellheaded – never got, you know, swagly.” When Boring’s wife had a baby, Truman went to the hospital to visit her and the newborn. One Christmas when he was back home in Independence, Truman was aghast to learn that several agents assigned to him were standing outside in the snow. Truman invited them to the back porch to dry off. (Several years later, when agents assigned to President Eisenhower asked him if they could stand on the back porch of his cabin during a downpour, Ike answered, “Nothin’ doing.”)

Truman sometimes bristled at the restrictions the Secret Service imposed upon him. At the same time, he understood the need for security. The Secret Service recorded nearly 2,000 written or oral threats against him and his family in 1949 alone. And the following year, he was the target of a very serious assassination attempt.

It took place on November 1, 1950. At the time the White House was undergoing extensive renovations, so the Trumans were living across Pennsylvania Avenue, in a mansion called the Blair House. Around two o’clock that afternoon – while Truman napped inside – two Puerto Rican nationalists attempted to storm the residence and gun down the president. It was a bold but hopeless attempt to draw attention to their cause. They never got past the front door. In a furious two-minute gunfight that ensued just under Truman’s second-floor bedroom window, one of the would-be assassins, Griselio Torresola, was killed. (Truman would later commute the death sentence of the other gunman, Oscar Collazo, to life imprisonment. Collazo was released in 1979 and died in Puerto Rico fifteen years later.) The shootout also claimed the life of a uniformed Secret Service officer named Leslie Coffelt, making him the only member of the agency to be killed protecting a president. Awakened by the noise, Truman watched the surreal scene unfold from his second-floor bedroom window.

In the aftermath of the assassination attempt, much attention was drawn to the fact that the Secret Service – nor, indeed, any other law enforcement agency – was legally empowered to protect the president. At long last, Congress was moved to act. On July 16, 1951, Truman himself signed the bill authorizing the Secret Service to protect the president, his immediate family, the vice-president, and the president-elect. “Well,” the president said a little sarcastically, “it is wonderful to know that the work of protecting me has at last become legal.”